The present invention relates to a press with a very large working surface with a pressure cell which applies pressure to a resilient forming pad, the pressure cell, via the forming pad, pressing sheet-formed workpieces over a forming tool or form block in a working space below the forming pad to shape the workpieces in a required way. The pressure cell and the forming pad are arranged in a cavity in a tray-shaped press plate which is attached to an upper force-absorbing member in a press stand or frame. The form block is disposed in the cavity in a tray-shaped displaceable supporting member (hereafter referred to as the press tray) which, after insertion into the working space, together with the press plate and elements cooperating therewith in the press frame forms a closed volume. A pressure medium (e.g. oil) is then pumped into the pressure cell to expand the same and force the forming pad downwards against a workpiece to be formed.
During the pressing operation, the forming pad will influence the end wall portions of the press plate and the base of the press tray in an axially upward direction. Owing to the high working pressure used in modern presses--100 Mpa and thereabove--these forces will be very great and because of the stress intensification which arises at a transition zone between thicker and thinner regions of a plate subjected to heavy stress, the edge/end regions of the press plate and the base of the press tray will experience very high stresses which lower the fatigue life of those components.
Presses of the kind to which the invention relates are described, inter alia in the specifications of U.S. Pat. Nos. 3,875,778 (Hellgren), 3,938,361 (Claesson et al) and 3,949,583 (Syvakari) all of which have been assigned to the assignee of this application.